There are three types of peripheral hearing loss in children. Before discussing them, it will be
helpful to understand a brief overview of the human auditory system as a whole. In general, there are two parts of the human auditory system. They are the peripheral auditory system and central auditory system. Think of the central auditory system as the brain region where sound is truly processed and perceived. The central auditory system is supplied with auditory information from the peripheral auditory system which is made up of three distinct sections: the outer, middle, and inner ear. These sections are all designed to detect, collect, and organize the sounds we are able to hear and send them along the auditory pathway which travels up to the brain.
This process is not without complications and at times a hearing loss will be present in either the peripheral auditory system, central auditory system, or both. Our focus in this article will now shift to specifically the peripheral auditory system and the three types of hearing losses that can occur.
They are defined as a conductive hearing loss, sensorineural hearing loss, and mixed hearing loss. A conductive hearing loss is one in which there is physical breakdown, blockage, or disruption of sound transmission through any part of the peripheral auditory system. This may include the ear canal, ear drum, middle ear bones (known as the malleus, incus, and stapes), and even inside the inner ear where we would typically find a sensorineural hearing loss. A sensorineural hearing loss is present at the location of the inner ear where very delicate structures called outer hair cells are damaged and are unable to effectively detect the presence of sounds. Additionally, sensorineural hearing loss is present at the location of the auditory nerve where sound is transmitted to the central auditory system. Outer hair cell damage may be present across a range of frequencies thus resulting in a variety of hearing difficulties. A mixed hearing loss is when both a conductive and sensorineural hearing loss are present at the same time in the same ear.
There can be many symptoms of peripheral hearing loss depending on the specific diagnosis and perception by the individual patient. Symptoms are largely dependent on not only the type of peripheral hearing loss but also the severity of the hearing loss. As sound is affected or restricted more and more, typically the more pronounced the symptoms will be. Examples of these symptoms include, but are not limited to, the following: raising the volume on common devices like the television, phone, and stereos or radios; having trouble following spoken conversation, most commonly in situations with background noise; trouble hearing people or sounds at a greater distance; trouble understanding speech when not face-to-face; having trouble following conversation when multiple people are talking; often needing to ask others to repeat themselves; thinking that other people are always mumbling; bluffing, or faking that something is understood when it isn’t; appearance of inattentiveness or disinterest in a conversation; tendency to avoid conversations; misunderstanding some words but understanding other words well enough, causing sentences to appear to make no sense; needing people to speak more slowly; trouble identifying the location of where a sound is coming from; feeling fatigued or tired from having to concentrate on listening. The list goes on, however, these examples of symptoms are very common presentations that are brought up in clinical practice every day.
These symptoms may appear in anybody, however, they typically will be easier to spot and are more obvious in adults. Indications of hearing loss in infants, toddlers, and children vary from those mentioned above and aren’t always as obvious. When it comes to infants and toddlers, look for the following signs: does not react to loud sounds; does not seek out or appears unable to detect where sound is coming from; is not babbling or has stopped babbling and experimenting with making sounds; can babble but maintains doing so without advancing to more understandable speech; does not react to voices, even when being held; physical signs of hearing difficulties recognized at birth including a missing ear or ear malformation.
As children grow up and become school-aged, the signs and indications of hearing loss will change. Some examples for this age range include the following: does not follow simple commands or directions, either at home or at school; appears easily frustrated or experiences communications breakdowns; is falling behind with speech and communication skills; cannot understand what is being said to them without being looked at directly; cannot identify where sounds are coming from; appears or is exhausted at the end of school from having to concentrate on understanding speech all day; shows signs of behavioral problems or social difficulties; experiences problems keeping up at school or is showing poor grades or grades changing and getting worse.
It is clear that having a peripheral hearing loss is significantly problematic to the individual with the diagnosis as well as communication partners, whether they be family members, friends, personal or professional acquaintances, or even strangers in public. Managing and navigating how to appropriately and accurately react and respond to speech and sound is a basic human skill that is imperative to not only normal development but to quality of life as a whole.
So, when is it time to go see a doctor when you or a loved one suspects a hearing loss is present? It goes without saying that there will always be times when someone needs something repeated, extra volume is desired, someone is mentally occupied and not paying attention, or in general a sound is missed partially or entirely. Do not make a mountain out of a molehill. However, when patterns become recognizable that can be associated with a hearing difficulty, either by the individual experiencing the hearing difficulty or by someone else, when physical discomfort is reported, when a sudden change in hearing is detected, or when abnormal auditory perceptions are present, it is time to go see a doctor.
A good place to start in any scenario regarding when to see a doctor is when pain or discomfort is present. This can commonly occur in children who have an ear infection, either in the outer ear or middle ear space, but can also occur in adults. An outer ear infection is known as otitis externa, or Swimmer’s ear, because repeated exposure to water can make the ear canal more vulnerable to inflammation. It can be accompanied by ear aches, redness or swelling inside the ear canal, itchiness inside the ear canal, colored drainage from the ear canal, and/or unpleasant smell emanating from the ear canal. The ear may be very tender to the touch as well. Another cause of pain or discomfort in the ear canal (i.e. the outer ear) is when there is a significant buildup of ear wax, called cerumen, present resulting in an increase in pressure and even in a reduction in hearing ability. A middle ear infection may also be present. This is called otitis media and there are a few types. One is called acute otitis media, or AOM. Another is chronic suppurative otitis media, or CSOM. A third is called otitis media with effusion, or OME. These types of ear infections will require medical detection to diagnose because the human eye cannot effectively see past the eardrum. There is fluid of varying consistency and quantity behind the ear drum thus affecting the natural movement of the middle ear bones and reducing sound transmission down the auditory pathway. Sometimes, a whole in the ear drum may also be present. This is called a tympanic membrane perforation. It can commonly be caused by infection, trauma, or rapid changes in pressure. Mismanaged or recurrent perforations can lead to further auditory complications and diagnoses. Depending on the cause of the perforation, pain or discomfort may be present and hearing loss is also expected to present itself. All of these diagnoses are considered conductive hearing losses because they are physically impeding sound transmission, resulting in pain or discomfort, and warrant a visit to a doctor.
If pain isn’t present, a trip to a doctor may still be necessary to objectively determine whether a suspected peripheral hearing loss is present. The typical sensorineural hearing loss is a painless process, occurring very slowly and progressively over many years. Due to this gradual decline in hearing ability, recognition of a hearing difficulty is oftentimes missed or delayed for many years until signs discussed earlier are recognized by the individual or a communication partner. Objective verification of a person’s concerns can help demystify why there has been trouble hearing effectively and only until a trip to a doctor’s office is scheduled will accurate answers be available.
When it comes to infants and toddlers, however, a trip to a doctor is more imperative. Early identification of a hearing disorder and intervention is vital to the child’s development. This is because sound is so crucial to appropriate developmental milestones, language acquisition and production, and has social, emotional, and mental implications. The sooner a hearing disorder is identified, the better it is to act. When it comes to newborns, most states have funded programs to help detect hearing problems at birth. These are called Early Hearing Detection and Intervention programs. If a screening at the hospital after birth is failed, it is a very good idea to follow up with a doctor to ensure more thorough diagnostic measures are completed to come to a more accurate conclusion as to the nature of the failed screening.
As for school-aged children and adolescents, keep an eye on their attentiveness, social interactions, grades, ability to follow directions, and general mood. If there is a suspicion that one or more symptoms discussed earlier are presenting consistently, it is a good idea to pursue a thorough evaluation with a doctor.
When a trip to a doctor takes place, they will utilize a variety of tests to help determine the type, configuration, and severity of the hearing loss. This test battery is very accurate and crucial in determining the appropriate course of treatment or further recommendation to another health provider. In general, the test battery is broken down into two components: objective, functional measurement and subjective, behavioral measurement. Different age groups will also necessitate different testing strategies to identify and diagnose hearing loss. For newborns and infants, objective measurement is necessary because valid behavioral responses will be difficult or impossible to obtain. The two types of audiologic tests used for this type of diagnosis are otoacoustic emission (OAE) and auditory brainstem response (ABR). Otoacoustic emission testing is completed by placing an earphone into the ear canal. This device will produce a specific sound designed to elicit a response from the ear it is testing. With a microphone inside the ear tip, a sound is produced by the ear in response to the stimulation sound. This response sound will be recorded. This method will enable a doctor to determine whether the outer hair cells located in the inner ear are functional or not and it will help confirm whether the cochlea, the housing of the structures of the inner ear, is intact and healthy or if a hearing loss is suspected. The ABR is another objective, functional assessment of the entire auditory pathway from the outer ear up to the brainstem. This measurement requires delicate electrodes to be placed on specific parts of the head and ears to help measure the response of the auditory system to clicks or tones designed to stimulate the ear being tested. An ABR test is able to detect whether a peripheral hearing loss is present based on the results of the measured waveforms produced by the auditory system and measured by the electrodes. These two tests do not require any involvement from the newborn or infant and are thus desirable diagnostic tools for this population. They are also applicable in larger test batteries for more standard clinical practice when assessing toddlers, adolescents, adults, and geriatrics.
An additional and common objective measurement is immittance testing. This procedure involves testing the function and mobility of the eardrum as well as the auditory pathway via the combination of gentle pressure introduced to the ear canal and a series of loud tones designed to elicit a muscular reflex behind the eardrum. This test is able to help identify whether a disorder is present in the outer ear, middle ear, or inner ear and can also be used to compare one ear to the other. It is helpful in assessing young children for ear infections, monitoring their treatment regimens, and corroborating findings of additional battery measures to form a final diagnosis.
Objective measurements are vastly helpful, however, they only tell us about the function of the ear and auditory system, but not how a person is actually hearing. This is a very subjective aspect of the test battery but is necessary to understand how the sounds used to test someone are actually perceived. For children old enough to respond to sound but too young to engage in testing beyond that simple response, Visual Reinforcement Audiometry, or VRA, is utilized. Typically, VRA is used with children aged around 6 months through 2 to 3 years old or if other behavioral developmental delays are present. VRA works by “training” a child to respond to a sound presented to them either through earphones or a loudspeaker system inside of a sound booth. Sounds may be presented into either the right or left ear or from the right or left loudspeaker eliciting the child to turn toward the sound source. The child is then reinforced with the use of visual stimulations like animatronics and light up devices as a sense of reward for reacting to the sounds which are systematically lowered as much as possible to help find the softest sounds detectable at a range of frequencies. When children outgrow VRA but are still too young for more traditional behavioral measurements, another method is used, called Conditioned Play Audiometry, or CPA. With CPA, children are again wearing earphones or placed in a sound booth and are “conditioned” to respond to sound stimulation in either ear or from either loudspeaker by learning to play a game. An example of CPA is when a sound is heard the child is taught to drop a small toy into a bucket. Every time they hear a sound, no matter how soft, they drop another toy into the bucket. A variety of techniques are available and creativity is necessary in most cases to help keep the children engaged and attentive to the task at hand.
When children are old enough, usually around 6 years old but sometimes sooner, traditional audiometry can be utilized. This is the method of choice for audiologists to measure for what is called a behavioral threshold. Audiometry helps establish how well a person hears a range of frequencies. It will also help establish the configuration of a person’s hearing ability, meaning whether they hear certain frequencies better than others. Audiometry is done via two methods, air and bone. Air conduction testing tests for sounds passing through the entire peripheral auditory system while bone conduction testing tests for sounds going straight to the inner ear. The comparison of the responses from air and bone conduction testing will help establish whether a hearing loss is conductive, sensorineural, or mixed. A final aspect of the test battery is speech recognition measurements. These tests are designed to check for how well someone is able to understand speech sounds, not frequency specific sounds called pure tones. Speech testing is broken down into recognition of two syllable words, called spondees, at very soft levels to establish a speech recognition threshold, the ability to discriminate one word out of a sentence at louder, more audible levels to develop a percentage of word understanding ability, and the ability to understand a sentence of speech amongst background noise in order to measure how well someone is able to distinguish aspects of speech in challenging listening conditions. These latter speech measures are not designed to help diagnose a hearing loss, but rather are used to understand the effect of a hearing loss or rather hearing ability on daily function and communication. They are helpful in guiding recommendations for treatment and useful in measurement the outcomes of that treatment over time.
There has been a lot of discussion on the background of peripheral hearing loss, types of diagnoses, symptoms, and tests used to form the diagnoses, but what if it can all be prevented? Can peripheral hearing loss be prevented? The short answer is maybe. Prevention is dependent on the cause of the hearing loss in the first place. Causes can range from noise exposure, physical trauma, and ototoxic medications (medications that are toxic to the ear), to hereditary disorders, syndromes, and age-related hearing loss (called presbycusis). Some types of peripheral hearing losses can be prevented with the use of hearing protection, like noise induced hearing loss, as well as healthy listening habits like exposing oneself to loud noise for limited amounts of time. Other causes like age and hereditary factors are out of our control and cannot be prevented. What is helpful to know is that hearing is like any other part of the body and generally applicable healthy habits extend to the ear. This includes getting plenty of exercise, incorporating a healthy diet, and generally taking care of oneself. Doing so may help mitigate the effects of more detrimental habits related to hearing disorders, like smoking which can lead to small vessel disease and poor diet which can result in diabetes, both of which are related to peripheral hearing loss. In short, some aspects of peripheral hearing loss are preventable while others are not.
If a peripheral hearing loss ends up being diagnosed, treatment ranges depending on the diagnosis. The most common form of peripheral hearing loss by far is sensorineural hearing loss. Remember, this is when the outer hair cells inside the inner ear (cochlea) are damaged. There is no cure for a sensorineural hearing loss, and no pill or medication. The standard of care for treatment is the use of a specially fit and programmed hearing aid. This device will help accurately deliver sound to the peripheral auditory system and reintroduce, in a general sense, volume and clarity to the individual experiencing the hearing disorder. If the hearing loss is conductive or mixed in nature, then there is really good news in that treatment may absolutely include a true cure! Treatment is often started with a referral to a physician who can prescribe ear drops in the case of ear infections or perform a surgery in the case of middle ear complications or physical malformations. If surgery is ineffective, partially effective, or completely effective but a hearing loss remains due to the presence of a mixed hearing loss diagnosis, then additional audiologic treatment will be necessary. This can, of course, include hearing aids or even specialized bone-anchored devices or even a cochlear implant if the severity is profound enough.
On the horizon of audiologic care and management are exciting possibilities beyond that which are clinically utilized today. Research is underway on gene therapies to help restore and “cure” sensorineural hearing loss which, to our medical understanding today, is permanent and irreversible. Stem cell research has been a topic of conversation for many years as it relates to regeneration of outer hair cells and their associated anatomical components, including stereocilia, in an effort to reverse permanent sensorineural hearing loss that is presently only treated with amplification or cochlear implantation. Progress in understanding the genetic basis of hearing and the operation of the ear is crucial in guiding current and future research towards new therapies that can help restore normal or more normal peripheral hearing ability. However, since the ear is a very complex structure that is still requiring operational understanding, applying a gene therapy to restore part of all of its normal function is no easy task. Perhaps one day, gene therapy for treatment of sensorineural hearing loss will be the standard while the use of amplification will be a temporary component of the overall process, something to be utilized for intermediate use only, on the way towards restored inner ear function.
Other topics of discussion relating to peripheral hearing loss are focused on those with diagnosed autism spectrum disorder and whether there is a relationship between that diagnosis and hearing loss. The research on this topic is mixed. That is to say, some studies have shown that the estimated risk of ASD was higher in children with hearing loss relative to the general population while other studies have shown no conclusive evidence of increased hearing loss in children with ASD. Since determination of the presence of hearing loss in a child with ASD can be behaviorally difficult to obtain, clinicians can utilize objective and functional auditory brainstem response (ABR) testing to make a more informed determination. Some literature indicates hypotheses stating that sensory disturbances in ASD may be related to brainstem dysfunction. However, since ABR is not very sensitive to slight levels of hearing loss or low frequency hearing loss, it is necessary to use the acquired information in context with other holistic findings, such as immittance measures and otoacoustic emissions testing. In general, the majority of the literature on the topic indicates that there are increased rates of peripheral audiological dysfunction in individuals with ASD and that abnormal ABR findings related to audiological dysfunction in ASD have been very replicable among studies.
This was a comprehensive review of what constitutes a peripheral hearing loss, its three types, related symptoms in various patient populations, recommendations on when to seek out help from a doctor, how diagnoses are made and what tests help in that process, as well as a discussion on if peripheral hearing loss is preventable, treatment review for peripheral hearing loss, and new developments on the horizon pertaining to peripheral hearing loss gene therapies and understanding of its relationship to children with autism spectrum disorder.
